Revert "net: Only process 1 packet per ethernet RX interrupt"

This reverts commit acb35785c9.

It turns out that this commit actually causes problems if an ethernet
interrupt is dropped because a higher privilege task is running, such
as LocalFileSystem accesses.  If this happens, the semaphore count isn't
incremented enough times and the packet_rx() thread will fall behind and
end up running as though it had only one ethernet receive buffer.  This
causes even more lost packets.

I plan to fix this by switching the semaphore to be a signal so that
the syncronization object is more boolean.  It simply indicates if an
interrupt has arrived since the last time packet_rx() was awaken to
process inbound packets.

libraries/net/eth/lwip-eth/arch/lpc17_emac.c

@@ -812,8 +812,9 @@ static void packet_rx(void* pvParameters) {
         /* Wait for receive task to wakeup */
         sys_arch_sem_wait(&lpc_enetif->RxSem, 0);
 
-        /* Process packet for this semaphore signal */
-        lpc_enetif_input(lpc_enetif->netif);
+        /* Process packets until all empty */
+        while (LPC_EMAC->RxConsumeIndex != LPC_EMAC->RxProduceIndex)
+            lpc_enetif_input(lpc_enetif->netif);
     }
 }